In wireless communication, space propagation causes loss of an electromagnetic wave transmitted from an antenna of a transmitting apparatus before the wave is received by an antenna of a receiving apparatus. Such space-propagation loss depends not only on a distance from the antenna of the transmitting apparatus to the antenna of the receiving apparatus but also directivity of the antennas, materials of utensils existing in an actual communication environment, a positional relationship between the utensils, and the like. The loss accordingly varies much. Therefore, to achieve high quality communication, the receiving apparatus is required to control a gain of an amplifier depending on a received power level.
There are communication methods in which data is expressed as a signal level of a transmission signal, such as amplitude shift keying (ASK) and on-off keying (OOK). If such a communication method is used, the receiving apparatus has only to include at least one comparator. Therefore, the receiving apparatus can have a simpler configuration compared with a receiving apparatus used in a wireless LAN system according to IEEE802.11. However, there is a difficulty in determining whether a signal output from the comparator derives from a received signal or noise if only one comparator is provided. It may be difficult to control a gain so as to obtain a signal power adequate for demodulation processing.
A receiving apparatus using a communication method in which data is expressed as a signal level of a transmission signal is therefore demanded to be capable of controlling a gain of an amplifier so as to achieve a signal-to-noise ratio (SNR) required for demodulation processing.